The present disclosure relates to an analog-to-digital (AD) conversion apparatus employed in mainly a receiving apparatus used in a radio communication in addition to audio equipment and medical measurement equipment and also relates to a signal processing system making use of the AD conversion apparatus.
FIG. 1 is a diagram showing a rough configuration of an AD converter (ADC) 1.
In FIG. 1, reference notation X denotes an input voltage supplied to the AD converter 1. The input voltage X is an analog signal. On the other hand, reference notation Y denotes an output voltage generated by the AD converter 1. The output voltage Y is a digital signal.
The AD converter 1 generates distortions caused by non-idealities of circuit components employed internally in the AD converter 1. When the circuit components generate distortions, the output voltage Y generated by the AD converter 1 includes not only the fundamental wave component, but also harmonic components.
The even-order distortion components included in the harmonic components can be sufficiently attenuated by designing the AD converter 1 into a fully differential configuration. However, the odd-order distortion components included in the harmonic components are output by the AD converter 1 as they are.
If the AD converter 1 shown in FIG. 1 has a distortion characteristic, for an input voltage X small to a certain degree, the output voltage Y is expressed by Eq. (1) as follows.Y=a1X+a3X3+a5X5+ . . .  (1)
Reference notation ai used in the above equation denotes the gain of the distortion component of the ith order. It is obvious from the equation that the distortion components of the even order are not generated as described above.